I don't even see why people think of the release date of a new piece of application software as a "major event," or try to make plans (let alone hardware upgrades) in anticipation of what is basically interface software that has little if anything to interface WITH on the day it's first released.
The release of vista, or DX10 will mean very little until the software has come out for it. And the first software (including games) that come out advertising that they use new application features are always at least a little bit lame. And the first hardware that comes out is nearly always underpowered compared to what will be needed once the software catches up.
It will be several months before games come out that take significant advantage of the features. And it will be years (if ever) before games come out that truly RELY on the new applications, and before new hardware comes out that can truly play that new software the way it's meant to be played with all the new features turned on.
This is all an iterative processs. Every new advance is nice, but each one is just another tiny little ratchet in the huge wheel of progress, not some kind of major revolution the rest of the world has to drop everything and hop onto.
And that's all assuming the best case scenario. Doesn't anybody remember things like Microsoft ME, and that weird "Bob" thing? No matter who's pushing it, there's never a guarantee any operating system or application is going to catch on AT ALL, let alone become something you NEED.
The bottom line: IF you want to upgrade, then upgrade. And, all else being equal, if one video card advertises it makes better use of a brand new application, you might let that influence your buying decision a bit. But it will be a long time before any system or application coming out now will be something you really need to worry too much about.